In a typical wireless communication network, wireless devices, also known as wireless communication devices, mobile stations, stations (STA) and/or user equipments (UE), communicate via a Radio Access Network (RAN) to one or more core networks (CN). The RAN covers a geographical area which is divided into service areas or cell areas, which may also be referred to as a beam or a beam group, with each service area or cell area being served by a radio network node such as a radio access node e.g., a Wi-Fi access point or a radio base station (RBS), which in some networks may also be denoted, for example, a NodeB, eNodeB (eNB), or gNB as denoted in 5G. A service area or cell area is a geographical area where radio coverage is provided by the radio network node. The radio network node communicates over an air interface operating on radio frequencies with the wireless device within range of the radio network node.
Specifications for the Evolved Packet System (EPS), also called a Fourth Generation (4G) network, have been completed within the 3rd Generation Partnership Project (3GPP) and this work continues in the coming 3GPP releases, for example to specify a Fifth Generation ( 5G) network also referred to as 5G New Radio (NR). The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access network, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP radio access network wherein the radio network nodes are directly connected to the EPC core network rather than to RNCs used in 3G networks. In general, in E-UTRAN/LTE the functions of a 3G RNC are distributed between the radio network nodes, e.g. eNodeBs in LTE, and the core network. As such, the RAN of an EPS has an essentially “flat” architecture comprising radio network nodes connected directly to one or more core networks, i.e. they are not connected to RNCs. To compensate for that, the E-UTRAN specification defines a direct interface between the radio network nodes, this interface being denoted the X2 interface.
Multi-antenna techniques can significantly increase the data rates and reliability of a wireless communication system. The performance is in particular improved if both the transmitter and the receiver are equipped with multiple antennas, which results in a Multiple-Input Multiple-Output (MIMO) communication channel. Such systems and/or related techniques are commonly referred to as MIMO.
In addition to faster peak Internet connection speeds, 5G planning aims at higher capacity than current 4G, allowing higher number of mobile broadband users per area unit, and allowing consumption of higher or unlimited data quantities in gigabyte per month and user. This would make it feasible for a large portion of the population to stream high-definition media many hours per day with their mobile devices, when out of reach of Wi-Fi hotspots. 5G research and development also aims at improved support of machine to machine communication, also known as the Internet of things, aiming at lower cost, lower battery consumption and lower latency than 4G equipment.
5G is currently being standardized in 3GPP while at the same time LTE will continue evolving which means in a long run, LTE and 5G will coexist together. Tight interworking between LTE and 5G will provide better performance for end user and also save the cost for network operator. Then there will be several scenarios also referred to as architecture or connectivity options according to the standard to consider how 5G and LTE inter-work.
Currently there is also ongoing standardization of Next Generation Core Network, called NGCN or 5G-CN or similar. The NGCN will support connectivity of both 5G radio or NR, and LTE.
Some Definitions:
The wording non-standalone as used herein means using LTE as the control plane anchor for supporting NR 5G as an extra data boost carrier, which arrangement is also referred to as Dual Connectivity (DC), as compared to standalone NR 5G, which implies full control plane capability for NR 5G.
The wording master node when used herein means the node which is the control plane anchor. The control plane anchor handles initial connectivity and mobility for the UE such as a wireless device. The master node is also responsible for activating the secondary node, also referred to as setup DC. The wording secondary node when used herein means the node that provides user plane connectivity in addition to the user plane connectivity provided by the master node. The wireless device in DC is simultaneously connected to both the master and secondary node.
The radio protocol architecture for LTE is separated into a control plane architecture and a user plane architecture. In the user plane between the e-Node B and UE, the application creates data packets that are processed by protocols such as Transmission Control Protocol (TCP), User Datagram Protocol (UDP) and Internet protocol (IP). In the control plane, the Radio Resource Control (RRC) protocol creates signalling messages that are exchanged between the eNB and the UE. In both cases, the information is processed by the PDCP, the Radio Link Control (RLC) protocol and the Medium Access Control (MAC) protocol, before being passed to the physical layer for transmission.
The relevant options to the discussion in this document comprise the following Non-Standalone scenarios as specified in the standardized in 3GPP. The solid lines in the scenarios below represent use plane traffic and the dashed lines in the scenarios below represent control plane signaling connections.
Option 3) is depicted in FIG. 1. In this scenario, a wireless device is using NR as a secondary node and LTE as master node connected to EPC. In this scenario there is no direct user plane between EPC eNB and NR gNB instead NR traffic is routed via the LTE eNB.
Option 3a) is depicted in FIG. 2. In this scenario, the wireless device is using NR as a secondary node and LTE as master node connected to EPC. In this scenario there is a user plane A1 between EPC and the NR gNB. 1A in FIG. 2 means user plane connection.
Option 4) is depicted in FIG. 3. In this scenario, the wireless device is using 5G NR as a master node connected to NGCN. LTE eNB is a secondary node. In this scenario there is no direct user plane between NGCN and LTE eNB. LTE user plane is routed via 5G NR node.
Option 4a) is depicted in FIG. 4. Here the wireless device is using 5G NR as a master node connected to NGCN. The LTE eNB is a secondary node. In this scenario, a user plane between the NGCN and the LTE eNB is referred to as 1A like in FIG. 4, which means that the LTE eNB data is sent directly to the NGCN.
Option 7) is depicted in FIG. 5. Here, the wireless device is using NR as a secondary node and LTE as master node connected to the EPC. In this scenario, there is no direct user plane between the EPC eNB and the NR gNB; instead, NR traffic is routed via the LTE eNB.
Option 7a) is depicted in FIG. 6. In this scenario, the wireless device is using NR as a secondary node and LTE as a master node connected to the EPC. In this scenario, there is a user plane 1A between the EPC and the NR gNB. The annotation 1A like in FIG. 6 means user plane connection.
From a protocol perspective, the PDCP protocol for NR gNB would be different from that for LTE eNB, similarly, the Non-access stratum (NAS) protocol for 5G NGCN would be different from that for EPC, although they may be similar.
NAS is a functional layer in the UMTS and LTE wireless telecom protocol stacks between the core network and UE. This layer is used to manage the establishment of communication sessions and for maintaining continuous communications with the user equipment as it moves. The NAS is defined in contrast to the Access Stratum which is responsible for carrying information over the wireless portion of the network. A further description of NAS is that it is a protocol for messages passed between the UEs and core network nodes that are passed transparently through the radio network. Once the UE establishes a radio connection, the UE uses the radio connection to communicate with the core network nodes to coordinate service. The distinction is that the Access Stratum is for dialogue explicitly between the UE and the RAN and the NAS is for dialogue between the UE and core network nodes. For LTE, the Technical Standard for NAS is 3GPP TS 24.301.
That is, for a UE it can either connect to EPC or connect to 5G NGCN. Its master node may be either LTE eNB or NR gNB, and its secondary node may be either LTE eNB or NR gNB.
The problem is that as the UE may either connect to EPC or NGCN, its master node may be either eNB or gNB.